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TM4C1294NCPDT: PB1 description is unclear.

Mike Nudelman
Intellectual 295 points

Part Number: TM4C1294NCPDT

From the datasheet:

"All GPIO signals are 3.3-V tolerant, except for PB1 (USB0VBUS) which is 5-V tolerant."

Then

"Caution – All device I/Os pins, except for PB1, are NOT 5V tolerant; voltages in excess of the limits
shown in Table 27-6 on page 1820 can permanently damage the device. PB1 is used for the USB's
USB0VBUS signal, which requires a 5-V input."

 

There is a difference between "5V-tolerant" meaning the nominal voltage is whatever below 5V but will not damage the pin if it is 5V, and "Requires a 5V input" meaning that Vih should be within range for 5V and not 3.3V, else detection of logic "High" may not occur.

SO. Which one is it, when configured as USB0VBUS? Can I use a 3.3V high or do I need 5V?

 

  • 0
    TI__Mastermind 23715 points

    Hi Mike Nudelman

    All GPIO signals are 3.3-V tolerant, except for PB1 (USB0VBUS) which is 5-V tolerant. in page 1847 of device DS

    USB request VBUS 5V as input. USB0VBUS is arranged in PB1.

    So, PB1 and USB0VBUS should be the same meaning if you used USB. 

    >> Can I use a 3.3V high or do I need 5V?

    If you don't use USB. this GPIO can be 3V. if you use USB, USBVBUS should be 5V.

    Thanks!

  • 0 in reply to Xiaodong LI
    Intellectual 295 points

    Where exactly in the datasheet it lists Vih for the 5V-tolerant pin (PB1 configured as USB0VBUS), or the absolute maximum rating for it? I cannot find them.